using XPS and spray foam together in stud bay

I posted this in the insulation section but i need to get some fast answers and i know not a lot of people wander over there so i am going to post it here as well.

I have four of my rooms taken down to bare studs and i am about ready to insulate the exterior walls. I am really like idea of the spray foam but i hate the price. Can i first use 2" XPS board and then 1-1.5 inch of closed cell spray foam to get 3.5" of insulation and still retain the value of spray foam? This may be a stupid question but i have searched and searched and i cant find anything about it anywhere.

I am looking at the DIY spray foam kits and they are around $1400 for 1200 board feet. That comes to about 1.16 per foot not counting waste. Foam board is about $.50 per foot and is closed cell. If this would [COLOR=blue !important][COLOR=blue !important]work[/COLOR][/COLOR] would the spray foam stick to the smooth surface of the XPS?

by the way I am in nashville tn and the home is 1200 sqf main floor and a 1200 sqf basement (70% below grade) all brick/block.

Thanks
Brad

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Hi Brad, I think you are on the right track using a combination of foam and some other type of cheaper insulation. Research the following terms on the internet: "Hybrid Insulation System", "Flash and Fill Insulation" and "Flash and Batt Insulation". Also for anyone doing new construction check out this method of insulating: http://www.buildingscience.com/docum...s/high-r-value

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i have seem the flash and batt type of hybrid but i still havent seen a XPS version of it or if it has been tested. The problems i have read about with the flash and batt scare me with moisture issues. what i read talked about the vapor barrier being behind the fiberglass insulation and that could cause condensation in the wrong place.

My rooms are already gutted due to a moisture and what was starting to be a mold problem. I have corrected the moisture problem but now i am looking for the most efficent i can get will a medium budget. That is where the XPS and spray foam idea came from. Moisture can get past that (or should i say probably wont).

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?

Your Zone, if #4, requires only R-10 cavity insulation (minimum). I would be worried when adding the SPF after the rigid of being too low in the permanence rating of drying to the inside effectively. Rigid foam at 2" = 0.75 perms (about same as asphalt paper faced f.g.), SPF at 1-1/2" = 0.9 perms, combined let very little moisture through. Why so much foam? You want a vapor open inside (no poly), to dry both ways. When sunshine drives the water in the brick inward, you want a permeable cavity insulation not to stop the moisture in the cavity; http://www.buildingscience.com/docum...n-brick-veneer
Echo: http://www.greenbuildingadvisor.com/...moisture-walls

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If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent.
17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?